Field of the Invention
The invention relates to a device for holding sheets high in order to form gaps during operation of a pile-forming sheet-processing machine, in particular a sheet-fed printing machine.
In a pile-forming machine, the sheet pile that is produced has to be removed from time to time. Furthermore, in order for the printed image to be assessed, sample sheets have to be drawn out at regular intervals. In a continually operating machine, this should take place during operation as far as possible without disrupting production and without damaging sheets.
For this purpose, prior to the removal of a finished pile or of individual sample sheets, sheet interceptors, such as are described in the published German Patent Document DE 40 11 286 C2, are moved from the front, from between the front sheet stops, into the pile-forming region, with the result that the leading edge of the succeeding sheet, rather than dropping down onto the pile, is held high by the sheet interceptors. The gap which is thus kept open at the front side of the pile can then be utilized for removing a sample sheet or for sliding in an auxiliary pile carrier for pile-changing purposes.
In order to stabilize the free fall of the sheets as they are deposited on the pile, it is possible for the sheet falling height between the sheet brake, which brakes the sheets before they are deposited on the pile, and the top edge of the pile to be set by vertical adjustment of a sensor which registers the top pile edge and is linked to a lifting-control device for the pile base. In order for the sheets to be restrained reliably, in particular, in the case of great sheet-falling heights, the sheet interceptors are provided with a given minimum length by which they project into the pile-forming region. The printed image on the underside of the sheet is thereby damaged. Furthermore, the succeeding sheets make contact with the printed region of the preceding sheet and scratch the printed image thereof at the upper side. In the case of a very great falling height, however, the sheets are not reliably restrained by the sheet interceptors.
It is accordingly an object of the invention to provide a device for holding a sheet high, of the type mentioned in the introduction hereto which operates reliably for every sheet falling height, and helps to avoid scratching of the sheets. With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a device for holding sheets high in order to form gaps between sheets during operation of a sheet pile-forming sheet-processing machine, comprising vertically adjustable sheet interceptors for holding sheets high, the sheet interceptors being movable into a front pile-forming region so as to penetrate a depth therein which is so small that the sheet interceptors do not come into contact with a printed region of a sheet resting on the sheet interceptors.
In accordance with another feature of the invention, the holding device includes a common mounting support for the sheet interceptors and a sensor for registering a top edge of a sheet pile, the sheet interceptors and the sensor being arranged so that they are fixed relative to one another on the common mounting support, and the common mounting support being vertically adjustable as a whole.
In accordance with a further feature of the invention, the holding device includes front sheet stops also arranged on the common mounting support.
In accordance with an added feature of the invention, spacing of the sheet interceptors and the sensor relative to one another on the common mounting support is alterable for purposes of precision-adjustment.
In accordance with another aspect of the invention, there is provided a sheet-processing machine having a device for holding sheets high in order to form gaps between sheets during continuing operation of the machine, comprising vertically adjustable sheet interceptors for holding sheets high, the sheet interceptors being movable into a front pile-forming region so as to penetrate a depth therein which is so small that the sheet interceptors do not come into contact with a printed region of a sheet resting on the sheet interceptors.
In accordance with a concomitant aspect of the invention, there is provided a sheet-fed printing machine having a device for holding sheets high in order to form gaps between sheets during continuing operation of the printing machine, comprising vertically adjustable sheet interceptors for holding sheets high, the sheet interceptors being movable into a front pile-forming region so as to penetrate a depth therein which is so small that the sheet interceptors do not come into contact with a printed region of a sheet resting on the sheet interceptors.
By setting the sheet interceptors to the sheet fall height, the relative spacing between the sheet interceptors and the top pile edge can be kept constant. It is thus possible for the penetration depth of the sheet interceptors to be much smaller than when the latter are arranged in a fixedly predetermined manner.
By setting the sheet interceptors so that they penetrate into the pile-forming region just above the pile surface, reliable interception of the sheets is ensured, despite the small penetration depth, and the deformation of the high-held sheets is kept to a very low level. This avoids a situation wherein the sheets are damaged by buckling.
Separate readjustment of the sheet interceptors may be dispensed with if the sheet interceptors and a sensor which registers the top pile edge are arranged so that they are fixed relative to one another on a common mounting support which can be adjusted vertically as a whole.
Provision may thus be made for the front sheet stops likewise also to be arranged on the common mounting support.
For precise adjustment of the sheet interceptors, provision may be made for altering the spacing of the sheet interceptors and the sensor relative to one another on the common mounting support, for the purposes of precision-adjustment.
A sheet processing machine and a sheet-fed printing machine, respectively, which are equipped with the sheet interceptors according to the invention also form parts of the invention.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for holding sheets high, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: